Many clinical diagnostic methods require a blood sample from a subject. Blood samples include, for example, venous blood samples, arterial blood samples, capillary blood samples, and mixed venous blood samples. Obtaining a blood sample typically requires puncturing the skin of a subject. For example, arterial and venous blood samples are typically obtained by inserting a needle or catheter into an artery or vein in order to obtain arterial or venous blood samples (respectively). Mixed venous blood samples may be obtained from the pulmonary artery (requiring an invasive procedure). Arterial and venous blood samples thus require puncturing the skin of a subject, in order to insert a portion of a needle or catheter into an artery or vein. Blood may be obtained without a needle, for example, by puncturing the skin of a subject and collecting blood that exits the puncture site. For example, a fingerstick blood sample may be obtained by lancing a digit (e.g., a finger) of a subject and collecting one or more drops of blood from the wound in the digit. Depending on the type and size of puncture, the amount of blood required, the time to obtain a blood sample, the quality of blood samples may be variable.
However, many subjects find giving blood samples to be unpleasant and painful. Moreover, different methods, different personnel (e.g., phlebotomists), and different subjects may provide different amounts and different qualities of blood when sampled. Thus, in addition to causing discomfort or pain to subjects, present methods of obtaining blood samples may be inconsistent, or may provide variable amounts of blood, or may provide blood samples of inadequate quality or integrity. Accordingly, improved methods of obtaining blood samples from subjects are desired.